The present invention generally relates to a reading apparatus for reading images and more particularly, to an image reading apparatus employing a solid state image sensor for reading images such as characters, figures and the like.
Conventionally, the image reading apparatus of the above described type is, for example, used for reading images of an original in an electrophotographic copying apparatus, and is so arranged that an original to be read is placed on a transparent plate such as a glass plate or the like of an original platform and its image reading surface is illuminated by a suitable light source, while the image reading surface is scanned by a line-form solid state image sensor to obtain image information signals related to the original, which are converted into binary image signals so as to be successively stored in a memory means.
Incidentally, in the above case, the original to be read does not always occupy the entire area of the image reading surface of the original platform, while in many cases, not only some margins are present in the original, but the entire surface of the original is not necessarily read at all times.
In the conventional image reading apparatus as described in the foregoing, however, it is so arranged that the image signals for the entire surface of the image reading surface are stored in the memory means, and therefore, it has been necessary for the memory means to store signals for unnecessary portions where the original images are not present, thus requiring an unreasonably large memory capacity, with a consequent increase in the size and manufacturing costs for the image reading apparatus.
Additionally, in the known image reading apparatus of the above described type, such inconveniences often take place that, due to the deterioration with time of the light emitting characteristics of the lamp used for illuminating the original and of the photoelectric conversion characteristics of the solid state image sensor, or due to fluctuations of the functioning characteristics at the starting of the lamp, solid state image sensor, etc., the shading of the illuminated image to be read becomes unstable, thus obstructing thecorrect reading of the image. For preventing malfunctions in the image reading as described above, a means for detecting the amount of light amount of the lamp is separately provided so as to control the light emitted from the lamp, but such an arrangement is also disadvantageous in that the lamp light amount control mechanism is complicated, with a consequently high cost.